This invention relates mainly to cement clinker and method for manufacturing the same, or cement composition containing the cement clinker, as well as method for treatment of waste containing alkali components for use as a cement raw material.
In these years, recycling of wastes has arisen as a critical issue in view of global environment protection regardless of whether it belongs to government or industrial circle. Along with this situation, the cement industry has been positively promoting the recycling of wastes through the use of fly ash or blast-furnace slag as blended cement, or of various wastes as cement raw materials, and is expected to play an important role in the waste recycling.
Recently, there have been carried out various studies such as on xe2x80x9cEco-Cementxe2x80x9d to use chlorine-containing waste such as municipal solid waste as a raw material for special cement, and xe2x80x9cCompletely-Recycled-Cementxe2x80x9d to make up the recycling system which enables the manufacturing of cement by using only the recyclable materials as cement raw materials and the reuse of the same as cement raw materials after served.
However, the statistical fact is that 25 million tons of concrete waste is generated per year, of which 10 million tons are used as roadbed materials, while 15 million tons are thrown out. As a part of xe2x80x9cDevelopment of Techniques to Suppress Generation of Construction Byproducts and Recycle the Samexe2x80x9d (1993-1994), a total technical development project of Japanese Ministry of Construction, a joint study on xe2x80x9cDevelopment of Utilization Technique of Recycled Concretexe2x80x9d was carried out, through which steady movement towards the recycling proceeds. However, there still remain numbers of problems on recycling of concrete waste as a recycled aggregate.
One of the problems arises in reusing fine particles worn out and removed from the surface of an aggregate during the recycling process for manufacturing a recycled aggregate of good quality. Considering the possibility to reuse fine particles as a cement raw material in the recycling method, it is appeared that the reusing of the fine particles as cement raw material is hardly achieved since alkali components contained in the fine particles deteriorate the flow ability of cement in association with the fact that the content of alkali components is 0.75% or less, a value prescribed by JIS.
Glass waste, sludge cake of bentonite used in building operations, or the like also poses a problem due to an excessive amount of alkali components contained therein when used as a cement raw material. Specifically, while an established system for reuse of glass waste by crushing it into cutlet exists, the reuse of colored glass is limited. Accordingly, there is a demand to the reuse of colored glass as cement raw material. However, these wastes also contain a large quantity of alkali components likewise the treatment of fine particles generated during manufacturing recycled aggregate, so that the a possibility to reuse these wastes as cement raw materials is greatly lowered.
It is an object of the present invention to suppress deterioration of the flowability, as well as simultaneously enhancing the hydration of belite or the like mainly comprised of C2S, when alkali components have been incorporated into cement, thereby attempting effective use of waste containing alkali components as a cement raw material.
Considering the utilization of an alkali component-containing waste as a cement raw material, there remains a possibility to reuse the same, as far as the conditions that (i) a reactive aggregate is not used when cement is used as mortar, concrete or the like, and (ii) the prescribed value of the content of alkali components in cement is relaxed are met. Particularly, the incorporation of the alkali component-containing waste into a cement raw material with a large quantity of belite formed therein increases the solid-solution amount of alkali components in belite during the firing operation, thereby improving an inherently low hydration reactivity of belite. This improvement of the hydration reactivity leads to enhancement of a middle- and long-term strength development of cement, and hence is considered as a reasonable solution.
However, where the content of alkali components in a normal belite cement is increased, although there is produced a positive effect that the hydration is enhanced by the solid solution of alkali in belite, the alkali solid solution simultaneously occurs in a calcium aluminate phase whose hydration reactivity is inherently high. Accordingly, the hydration reactivity in the calcium aluminate phase is increased. This poses a new problem of lowering the flowability of cement paste, mortar, concrete or the like in actual use.
The present inventors have repeatedly studied in earnest to solve the above problem, and found that through the adjustment of the mass ratio of Al2O3/Fe2O3 in cement clinker, the ratio of the content of alkali components to the content of belite, and the ratio of Na2O to K2O in alkali within predetermined ranges suppresses the lowering of the flowability while enhancing the hydration reactivity of belite. Thus, the present invention has been achieved.
According to the present invention, there is provided cement clinker which is characterized in that it comprises Al2O3 and Fe2O3 wherein the mass ratio of Al2O3/Fe2O3 is 0.05-0.62, and alkali components and C2S wherein the content Y (mass %) of alkali components and the content X (mass %) of C2S satisfy the formula: 0.0025X+0.1xe2x89xa6Yxe2x89xa60.01X+0.8.
The content Y of alkali components and the content X of C2S are respectively represented in mass % of the content of alkali components and C2S to the total mass of the cement clinker.
According to another aspect of the present invention, there is provided cement clinker which is characterized in that it comprises Al2O3 and Fe2O3 wherein the mass ratio of Al2O3/Fe2O3 is 0.05-0.62, and alkali components and C2S wherein the content Y (mass %) of alkali components and the content X (mass %) of C2S satisfy the formulae:
0.0025X+0.25xe2x89xa6Yxe2x89xa60.01X+0.8 when 0.05xe2x89xa6Al2O3/Fe2O3xe2x89xa60.3,xe2x80x83xe2x80x83(1)
and
0.0025X+0.25xe2x89xa6Yxe2x89xa60.01X+0.65 when 0.3xe2x89xa6Al2O3/Fe2O3xe2x89xa60.5.xe2x80x83xe2x80x83(2)
Also, in the cement clinker of the present invention, the mass ratio of Na2O to K2O of the alkali components preferably satisfies the formula: 0xe2x89xa6Na2O/K2Oxe2x89xa60.45
According to another aspect of the present invention, there is provided a cement composition which is characterized in that the aforesaid cement clinker is mixed thereinto.
According to still another aspect of the present invention, there is provided a method for manufacturing cement clinker that comprises incorporating Al2O3 and Fe2O3 at the mass ratio of Al2O3 to Fe2O3 being 0.05-0.62, incorporating alkali components and C2S with the content Y (mass %) of alkali components and the content X (mass %) of C2S satisfying the formula: 0.0025X+0.1xe2x89xa6Yxe2x89xa60.01X+0.8, and firing the resultant.
According to another aspect of the present invention, there is provided a method of treating waste containing an alkali components, which is characterized in that it comprises incorporating Al2O3 and Fe2O3 at the mass ratio of Al2O3 to Fe2O3 being 0.05-0.62, incorporating alkali components and C2S with the content Y (mass %) of alkali components and the content X (mass %) of C2S satisfying the formula: 0.0025X+0.1xe2x89xa6Yxe2x89xa60.01X+0.8, and firing the resultant.
In the method of the present invention, the mass ratio of Na2O to K2O in the alkali components preferably satisfies the formula: 0xe2x89xa6Na2O/K2Oxe2x89xa60.4.
It is possible to manufacture the cement clinker containing alkali components by incorporating alkali components into a cement raw material and firing the resultant. It is presumable that the alkali components in the cement clinker exist mainly in a solid solution form within a so-called cement clinker mineral such as C3S, C2S, C3A, and C4AF. Therefore, once the alkali components are solid-dissolved in the cement clinker mineral, a cement composition has an unstabilized structure which leads to a high hydration reactivity.
That is, by the incorporation of alkali components in the cement clinker with Al2O3 and Fe2O3 contained at a mass ratio of Al2O3/Fe2O3 of 0.05-0.62 to have the content Y (mass %) of the alkali components and the content X (mass %) of C2S satisfying the formula: 0.0025X+0.1xe2x89xa6Yxe2x89xa60.01X+0.8, it is possible to enhance through the above action an inherently low hydration reactivity of C2S.
However, the incorporation of an excessive amount of the alkali components causes the alkali components to be solid-dissolved in a calcium aluminate phase whose hydration activity is inherently high. This further enhances the hydration reactivity, so that the flowability in the initial stage of the kneading operation of cement is lowered.
Accordingly, the generation of a calcium aluminate phase can be suppressed by having Al2O3 and Fe2O3 in cement clinker at a mass ratio of Al2O3/Fe2O3 of 0.05-0.62, while a belite phase can be activated through the solid-dissolution of alkali components effected by the incorporation of the alkali components to have the content Y (mass %) of the alkali components and the content X (mass %) of C2S satisfying the formula: Yxe2x89xa60.01X+0.8. Further, it is possible to suppress the lowering of the flowability in the initial stage of the kneading operation of cement due to the increased hydration reactivity of a ferrite phase by suppressing excessive solid-dissolution of the alkali components in the ferrite phase.
It is more preferable to have Al2O3 and Fe2O3 in the cement clinker at a mass ratio of Al2O3/Fe2O3 of 0.05-0.5 with the content Y (mass %) of the alkali components and the content X (mass %) of C2S satisfying the formulae:
0.0025X+0.25xe2x89xa6Yxe2x89xa60.01X+0.8 when 0.05xe2x89xa6Al2O3/Fe2O3xe2x89xa60.3,xe2x80x83xe2x80x83(1)
and
0.0025X+0.25xe2x89xa6Yxe2x89xa60.01X+0.65 when 0.3xe2x89xa6Al2O3/Fe2O3xe2x89xa60.5,xe2x80x83xe2x80x83(2)
thereby more effectively suppressing the lowering of the flowability in the initial stage, while further promoting the hydration reaction of C2S.
Herein, alkali metal elements such as Na or K can be cited as alkali components contained in waste. These are generally contained as an alkali metal oxide such as Na2O or K2O. The form of the alkali components existing in the cement clinker is not necessarily limited to the solid solution form in the cement clinker.
As examples of the waste containing the alkali components, it can be cited without limitation soil deposited on the bed of a dam, river or lake, a refining slag and various fused slag in addition to the aforementioned concrete waste, glass waste and sludge cake.
It is also possible to use any material other than wastes, as far as it contains alkali components.
The present inventors have also repeatedly studied to clear the difference of the actions of the respective types of the alkali components, and consequently found that when comparing Na2O with K2O, the dissolved amount of Na2O in the ferrite phase is larger than that of K2O, while K2O easily generates sulfates and the dissolved amount thereof in the ferrite phase is smaller. That is, it has been found that Na2O is a component which has a large influence to the lowering of the flowability of cement.
Accordingly, it is possible to enhance the flowability of cement through the suppressed dissolution of the alkali components in the ferrite phase, as well as enhancing the hydration reactivity of a belite phase through the promoted solid-dissolution of the alkali components in the belite phase by adjusting the mass ratio of Na2O to K2O in the cement clinker to satisfy the formula: 0xe2x89xa6Na2O/K2Oxe2x89xa60.45.
The alkali components are fired along with a cement raw material, and is contained in a solid solution form in a cement clinker mineral or in the form of an alkali metal sulfate such as Na2SO4 and K2SO4 or an alkali metal chloride such as NaCl and KCl.
As an example of the method for adjustment of the content of alkali components in the cement clinker, it can be cited a method including previously measuring the content of alkali components in an alkali-containing raw material (waste or the like), and incorporating the alkali-containing raw material into a cement raw material while simultaneously adjusting the content of alkali components in the alkali-containing raw material.